A satellite equipped with infrared cameras led to an amazing discovery: archeologists were able to see, for the first time, some of Egypt's long-buried pyramids. Find out how infrared scanning revealed over 3,000 ancient structures deep underneath the sand.

Infrared is often thought of as the same thing as heat. It's not. Heat is the measure of the overall 'jiggling' of a bunch of atoms. The faster they jiggle, the hotter it is. Heat radiates outwards because those atoms smash into other atoms, and spread the motion outwards. Infrared is a kind of light. It does not need to travel through a medium in order to get places, and so if a certain medium isn't right for it, it can simply pass through it without being absorbed.

Over in Egypt, it can pass through layers of sediment, through the atmosphere, and up until it is caught by the photoreceptors of a camera mounted on a satellite. And the kind of infrared light that is captured can let people analyzing the resulting picture know what's under the sand. Solar radiation makes its way down through the top soil, and sometimes geothermal radiation moves up, warming things under the sand. This can make all of the objects under the sand give off infrared light. (Although infrared light is not heat, it can be caused by heat in the same way that heating metal will make it glow red with visible light.) If there is nothing under the sand but more sand, the infrared light will be of a certain kind. If there is solid rock under the sand, it will give off a different intensity of infrared light. If there are clay dwellings, or bone scraps, they will give off yet a different kind of infrared.

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By flying such satellites over Egypt, over 3,000 buried structures have been revealed. Some exploratory excavations uncovered clay houses, but it also looks like there could be between two and seventeen pyramids, and the remains of an entire city under the sand. This could usher in a new age of excavation, in Egypt, and elsewhere.